Tunnel boring machines (TBM) are used to excavate circular cross section tunnels through a variety of soil and rock strata. As tunnels are bored regardless of geology, it is imperative the TBM and resulting excavating tunnel stay on the design alignment within the mandated tolerances. It may be very costly if 1. The tunnel veers off alignment wandering outside of the client's purchased Right-of-Way (ROW), 2. The TBM encounters unanticipated geological features or utilities in urban settings, or 3. The tunnel alignment and correction curves exceed the tight tolerances required for sustaining the dynamic envelope of train tunnels and highway tunnels. In order to avoid negative impacts on the TBM, the tunnel surroundings, or underground utilities, it is imperative that TBM be precisely locatable and guided when boring through the earth.
In addition to the need for precise navigation of the TBM, the tunnel itself must be mapped. The need for mapping in tunnels is twofold. Firstly, an as-built map of the tunnel is needed to compare finished tunnel dimensions to plan requirements. Secondly, the as-built map can be maintained after the tunnel is completed and used as a baseline measurement for reference during subsequent surveys to observe changes in tunnel geometry over time.
The present methods of TBM guidance primarily use lasers and conventional surveying techniques. Lasers and transit theodolites, originating from the tunnel entrance, are relayed through a network of fixed monuments on the tunnel walls and used to identify the position and attitude of the TBM relative to the desired design location. The precision in identifying the exact location (Northing, Easting, Elevation) of this progressive series of monuments and their growing error as the tunnel extends can lead to improper alignment of the tunnel or missing the end target within the stipulated tolerance. This conventional system using sighted theodolites to advance the monuments used by the laser guidance systems is often adversely affected by error inherent to accuracy of the measuring instruments, light refraction, angle of incidence, and reception. From the final measured monument near the TBM, a servo theodolite with distance measuring capability, along with inclinometers on the TBM, are used to identify the axis of the TBM as well as monitor TBM pitch (up and down), yaw, and rotation depending on their installation orientation. The theodolite locates and reports to the underlying guidance computer prisms attached to the TBM with a known orientation and location relative to the reference frame of the TBM. The motorized station can measure their location as the TBM bores the tunnel. The output from the inclinometers and updated target locations is relayed to a central processing unit which outlines the path for the TBM. Monitoring of TBM vertical alignment is derived from the same methods of angle and distance measurement. The series of monuments affixed to the tunnel wall as the TBM advances is measured for elevation using wire line water level instruments to minimize the accumulation of error relative to elevation. Gyroscopes may also be used to monitor the yaw of the TBM, verified by a surveyor.
The present state of tunnel mapping utilizes a two-step method. Firstly, the mapping positions are precisely located in reference to a known point outside of the tunnel. This is accomplished using a theodolite measurement device. If the tunnel curves, mirrors are used to reflect the beam, and the mirrors' locations are measured by the laser measurement device. Each of these mirrors induces additional error in the final measurement of the mapping positions. With the location and orientation of the mapping stations known, the tunnel walls are then measured at several locations with respect to this position. These measurements are typically done using reflector-less laser measurement system; however, other touch-less measurement systems, such as Electronic Distance Measurements (EDM), may be used to measure the distance to the tunnel walls.
The process of establishing the mapping locations and obtaining measurement is repeated until the entire tunnel has been measured. The distance measurements are then associated with their respective locations to generate a three dimensional map of the tunnel. This process is costly, time-consuming, and labor-intensive, requiring cessation of any work and traffic in the tunnel until survey completion.
What is needed is an integrated navigation system that provides real-time parametric guidance information to the TBM, relative to the tunnel origin (hereinafter “the pit”), past course, and current trajectory, while simultaneously employing a non-contact measuring system in concert with said origin and course information for the final provision of an as-built map of tunnel dimensions and centerline. The pit is a known point within the earth-centered-earth fixed global positioning system (GPS), and at least one of GPS retransmission and time modulated wireless triangulation architectures provide availability of positioning signals in the otherwise unavailable underground environment of a newly excavated tunnel. As the TBM proceeds along its excavation heading, a vehicle such as a rubber wheeled vehicle or a locomotive delivers ring assemblies, fabricated on-site in the pit to support the recently excavated portion of the tunnel. The constrained curvilinear path, also known as the design centerline, from pit to TBM is regularly traversed by the locomotive which is, in current systems, employed for transport of ring assemblies and muckout.